THE second collapse of some of the repairs to a section of the Pacific Highway near Tyndale was caused by vibrations from the machinery installing piles to bind the riverbanks, the RTA said yesterday.
A Roads and Traffic Authority (RTA) spokesperson said the collapse on Friday had not caused any delays and the section of road affected was due to be replaced anyway.
“The repair work involves the installation of large piles and backfilling,” the spokesperson said.
“Work to install piles creates vibration and some of that vibration caused a minor slip last Friday.
“The section of road surface that was affected by the slip was going to be replaced anyway and this has not caused any delays.
“The work is expected to be finished before Christmas.”
A 50-metre section of the riverbank, including the highway verge, collapsed into the river on June 14 after floods in late May and early June. The highway was closed for several days.
A combination of the floodwater and a burst water pipe was the cause of the collapse.
Initially the RTA predicted repairs would take weeks, but that increased to months when more of the riverbank fell into the water two weeks later.
“They think it’s going to take up to three months to fix it,” the RTA said at the time.
The delays increased further in September when much of the repair work collapsed again
A witness said all the repairs done since the original collapse had fallen away.
The Daily Examiner understands that the former Maclean Shire Council hired a firm to do studies of riverbank slippage in its region after floods.
In simple terms, the falling groundwater levels after flooding cause soil instability and the potential for the banks to slip into the river.
The report noted instances of this at Woodford Dale and Palmers Island.
The problem occurs on the outside bends of the river, where the action of the current destabilises the riverbank.
Update your news preferences and get the latest news delivered to your inbox.